بررسی آزمایشگاهی رفتار بار- تغییرمکان شمع‌های‌ پافیلی تحت بارهای کششی مایل در خاک ماسه‌ای

نوع مقاله : مقاله کامل پژوهشی

نویسندگان

گروه عمران، دانشکده مهندسی، دانشگاه بوعلی‌سینا

چکیده

پی‌های عمیق عموماً برای تحمل بارهای فشاری سنگین و انتقال بار از سطوح ضعیف خاک به لایه‌های عمیق‌ و مقاوم‌تر زمین استفاده می‌شوند. باتوجه به افزایش ضرورت ساخت سازه‌هایی نظیر برج‌های انتقال نیرو و دودکش­های بزرگ که علاوه بر تحمل بارهای فشاری سنگینی، در معرض نیروهای بالارانش قائم و مایل بزرگی همچون بارهای باد و زلزله نیز قرار دارند، محققین به‌دنبال بررسی راه‌حل‌هایی برای مقابله با این نیروها هستند. استفاده از شمع‌ها به‌عنوان مهار جهت مقابله با بارهای کششی مایل و قائم، باعث گسترش مطالعه رفتار کششی و بررسی عوامل مختلف مؤثر بر ظرفیت بالارانش شمع‌ها، در سالیان گذشته شده است. در این پژوهش توسط دستگاه ساخته ‌شده در دانشگاه بوعلی‌سینا، مطالعه آزمایشگاهی رفتار مدل‌های شمع ساده و پافیلی واقع بر بستر خاک ماسه‌ای با دانسیته نسبی 60%، تحت بار‌های کششی انجام گرفته و اثر پارامتر‌های مختلف شامل زاویه اعمال بار و نسبت قطر پافیلی به قطر شمع بر رفتار بار- جابه‌جایی مطالعه شد. مدل‌های شمع‌ با زوایای صفر (قائم)، 30، 60 و 90 درجه (افقی)، نسبت به محور شمع تحت کشش قرار گرفته و سپس پاسخ بار- جابه‌جایی به‌دست آمد. بر پایه نتایج تحقیق، مقادیر زوایای بحرانی بارهای کششی مایل تحت پارامترهای مختلف که به‌ازای آن حداکثر ظرفیت باربری شمع تحت بار کششی حاصل می‌شود، تعیین شد؛ زاویه بحرانی متناظر با حداکثر ظرفیت کششی، 60 درجه به‌دست آمد. تحلیل نتایج مطالعه نشان داد که ظرفیت باربری قائم نهایی شمع‌ پافیلی نسبت به شمع‌ ساده و همچنین با افزایش قطر قسمت پافیلی شمع، به‌طور قابل‌توجهی افزایش می‌یابد.

کلیدواژه‌ها


عنوان مقاله [English]

Experimental Investigation of Load- Displacement Behavior of Enlarged Base Piles under Oblique Tension Loadings in Sandy Soil

نویسندگان [English]

  • Masoud Makarchian
  • Erfan Matini
  • Sajjad Gholipour
Faculty of Engineering, Bu-Ali Sina University, Hamedan
چکیده [English]

One of the most used deep foundations are piles. The piles are tall members that are used to transfer the foundation loads from the weak layers of the soil to the ground at a deeper and stronger layers. In some structures, the piles may be exposed to uplift forces, including those subjected to extreme overturning moment, such as power towers or docks. During numerical modeling in relation to vertical pile under axial load, it was observed that the axial load bearing capacity of the pile was reduced at the presence of lateral loading (Abdel-Rahman and Achmus, 2006). For the pile under load, the ultimate vertical load ratio (p < sub>u) to the lateral loading (p < sub>L) was greater than 1, with a maximum resistance to load times, when the load angle was 30 degrees. The ratio p < sub>u/p < sub>L was between 0.18 and 0.72, and for the angle of 60 degrees, p < sub>u/p < sub>L less than 0.18 ratio, the ratio value is maximized at 90 degrees (Chattopadhyay and Pise, 1986). Baki et al. (2013) reported that the optimal load bearing of the piles under tensile loading is achieved in rough piles in anchored sand. By changing the angle of application of the tensile loading from zero to 60 degrees relative to the vertical, the pile frictional resistance only turns to the side resistance with the lateral side of the earth, and both components contribute to the final capacity. The study of piles behavior under oblique tension loadings showed that tensile loads are depending on the buried length ratio (L/d), the ratio of the enlarged base diameter to the pile diameter (B/d), the loading angle (α) and the relative density of the soil around the pile (Dr). The ultimate resistance of pile increases with increasing the ratios of (L/d), (B/d) and soil density. The analysis of the results showed that the critical angle (αcr) which the pile reaches its maximum tensile strength depends on the ratio (L/d), (B/d) and soil density (Mandal et al., 2002). The tensile load capacity of the buried enlarged base pile in the sand was studied using physical modeling tests. Analysis of the results showed that the uplift tensile capacity of pile increases significantly with increasing the ratio of buried length to pile diameter more than two and also, increasing the relative density of the sand. The results also showed that the increase in the pile diameter leads to tensile load of the pile (Nazir et al., 2015). A series of laboratory study and numerical analysis of finite element were performed to evaluate the efficiency of enlarged base piles with increasing cross-section at different levels of the pile length in order to improve its uplift capacity. The results of the study showed that with increasing the cross-section of the pile at different levels, the tensile capacity of piles increased, and the amount of sand deformation around the pile decreased (Moayedi and Mosallanezhad, 2017).

کلیدواژه‌ها [English]

  • Laboratory models
  • Enlarged Base Pile
  • Oblique load
  • Pile Bearing Capacity
  • Critical Angle
فخاریان ک، اسلامی ا، "ظرفیت باربری محوری شمع‌ها"، انتشارات پژوهشکده حمل و نقل، 241، 1384.
Abdel-Rahman K, Achmus M, “Numerical Modelling of the Combined Axial and Lateral Loading of Vertical Piles”, Institute of Soil Mechanics & Foundation Engineering and Waterpower Engineering, University of Hannover, Germany, 2006.
ASTM 2006, “Standard practice for classification of soils for engineering purposes (Unified Soil Classification System)”, ASTM standard D2487, West Conshohocken, PA, 2006.
Azzam WR, Elwakil AZ, “Model Study on the Performance of Single-Finned Pile in Sand under Tension Loads”, International Journal of Geomechanics, 2017, 17 (3).
Baki B, Ahmet D, Mustafa L, Bahadır O, Talha S, “An Investigation of Uplift Behavior of Vertical Piles Embedded in Reinforced Sand under Inclined Loads”, 2nd International Balkans Conference on Challenges of Civil Engineering, BCCCE, 23-25 May, Epoka University, Tirana, Albania, 2013.
Broms BB, “Lateral Resistance of Piles in Cohesive Soils”, Journal of the Soil Mechanics and Foundations Division, ASCE, 1964, 90, 27-63.
Chattopadhyay BC, Pise PJ, “Uplift Capacity of Piles in Sand”, Journal of Geotechnical Engineering, 1986, 112 (9), 888-903.
Chen JY, Gilbert RB, Puskar FJ, Verret S, “Case Study of Offshore Pile System Failure in Hurricane Ike”, Journal of Geotechnical and Geoenvironmental Engineering, 2013, 139 (10), 1699-1708.
Das BM, “Principles of Foundation Engineering”, 4th Edition, PWS Publishing Company, Pacific Grove, USA, 821p, 1999.
Dickin EA, “Uplift behaviour of horizontal anchor plates in sand”, Journal of Geotechnical Engineering, ASCE, 1988, 114 (11), 1300-1317.
Faizi K, Kalatehjari R, Nazir R, Rashid ASA, “Determination of pile failure mechanism under pullout test in loose sand”, Journal of Central South University, 2015, 22, 1490-1501.
Han F, Prezzi M, Salgado R, Zaheer M, “Axial Resistance of Closed-Ended Steel-Pipe Piles Driven in Multilayered Soil”, Journal of Geotechnical and Geoenvironmental Engineering, 2017, 143 (3).
Kong, GQ, “Performances of Compressive Capacity for Belled Wedge Pile Group”, in: Advances in Building Materials, Pts 1-3, Trans Tech Publications Ltd, Stafa-Zurich, 2011, 1084-1088.
Kong GQ, Yang Q, Liu HL, Liang RY, “Numerical Study of a New Belled Wedge Pile Type under Different Loading Modes,” European Journal of Environmental and Civil Engineering, 2013a, 17 (S1), 65-82.
Kong GQ, Cao ZH, Zhou H, Sun XJ, “Analysis of Piles Under Oblique Pullout Load Using Transparent- Soil Models”, Geotechnical Testing Journal, 2015, 38 (5), 725-738.
LoPresti, DCF, Pedroni S, Crippa V, “Maximum dry density of cohesionless soils by pluviation and by ASTM D 4253-83: A comparative study”, Geotechnical Testing Journal, 1992, 15 (2), 180-189.
Lutenegger AJ, “Uplift Tests on Shallow Cast-in-Place Enlarged Base Pedestal Foundations in Clay”, IFCEE, San Antonio, Texas, 2015.
Mandal AK, Patra NR, Pise PJ, “Behaviour of Enlarged Base Piles in Sand under Oblique Pullout Loads”, Indian Geotechnical Journal, 2002, 32 (4), 382-394.
Meyerhof GG, “Uplift Resistance of Inclined Anchors and Piles”, Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering, Moscow, 167-172, 1973.
Meyerhof GG, Adams JI, “The Ultimate Uplift Capacity of Foundations”, Canadian Geotechnical Journal, 1968, 5 (4), 225-244.
Moayedi H, Mosallanezhad M, “Uplift resistance of belled and multi-belled piles in loose sand”, Measurement, 2017, 109, 346-353.
Nazir R, Moayedi H, Pratikso A, Mosallanezhad M, “The uplift load capacity of an enlarged base pier embedded in dry sand”, Arabian Journal of Geosciences, 2015, 8, 7285-7296.
Niroumand H, Kassim KHA, Ghafooripour A, Nazir A, “Uplift Capacity of Enlarged Base Piles in Sand”, EJGE, 2012, 17 (R), 2721-2737.
Patra NR, Deograthias M, James M, “Pullout Capacity of Anchor Piles”, Indian Geotechnical Conference IGC, 2005.
Rad NS, Tumay MT, “Factors affecting sand specimen preparation by raining”, Geotechnical Testing Journal, 1987, 10 (1), 31-37.
Salgado R, “The Axial Resistance of Nondisplacement Piles”, Art of Foundation Engineering Practice Congress, West Palm Beach, Florida, United States, 2010.
Tehrani FS, Salgado R, Prezzi M, “Analysis of Axial Loading of Pile Groups in Multilayered Elastic Soil”, International Journal of Geomechanics, 2016, 16 (2).
Wen SL, “Failure Behavior of Belled Pile under Combined Loads”, Advances in Soil Dynamics and Foundation Engineering Conference, Shanghai, China, May 26-28, 2014.